1. Field of the Invention
The present invention relates to a lighting apparatus using microwave energy, and in particular to an electrodeless discharge lamp using microwave energy which is capable of being applied to various fields by having a compact construction.
2. Description of the Prior Art
An electrodeless discharge lamp emits lights by enclosing a certain amount of inert gas such as argon and materials such as halide, etc. generating plasmas and exciting them with microwave energy. The electrodeless discharge lamp has longer lifespan and shows better lighting efficiency than that of an incandescent lamp and a fluorescent lamp.
FIG. 1 is a longitudinal sectional view illustrating the conventional electrodeless discharge lamp using microwave energy.
As depicted in FIG. 1, the conventional electrodeless discharge lamp using microwave energy includes a casing 101 having a cylindrical shape, a magnetron 103 placed inside the casing 101 and outputting microwave energy, a wave guide 105 placed inside the casing 101 and transmitting the microwave energy, a mesh screen 119 installed to an outlet of the wave guide 105, cutting off the microwave energy and passing lights, a bulb 107 having enclosed inert gas (G) and placed at the central portion of the mesh screen 119, and a reflector 111 fixed to the casing 101 on the circumferential surface of the mesh screen 119 and reflecting lights generated in the bulb 107 toward the front.
The wave guide 105 is formed so as to have a regular square-shaped section in the travel direction of microwave energy in order to transmit microwave energy having a certain frequency, and a high voltage generator 113 is placed so as to be opposite to the magnetron 103 on the basis of the wave guide 105 (placed between them) and provides high voltage power.
A bulb motor 109 connected to the bulb 107 as one body and rotating it is installed to the lower portion of the wave guide 105.
A cooling fan 115 being rotated by the fan motor 116 is installed to the lower portion of the bulb motor 109 in order to cool the magnetron 103 and the high voltage generator 113.
An air guide 117 is formed at the circumference of the cooling fan 115 in order to provide air sucked from outside to the magnetron 103 and the high voltage generator 113 respectively.
The reflector 111 has an internal reflecting surface in order to reflect lights emitted from the bulb 107 toward the front.
In the meantime, microwave energy transmitted to a free space turns into a transmission mode traveling in a direction at a right angle to an electric field and a magnetic field, namely, a TEM (Transverse Electromagnetic) mode.
In contrast, microwave energy transmitted to through a wave guide travels while being reflected at a wall of the wave guide. The microwave energy can be a TE (Transverse Electric) mode at which only an electric field (E) is at a right angle to the travel direction and a magnetic field (H) is a transverse electric wave having elements in the travel direction, or the microwave energy can be a TM (Transverse Magnetic) mode at which only a magnetic field (H) is at a right angle to the travel direction and the an electric field (E) is a transverse magnetic wave having elements in the travel direction.
The TE mode, the TM mode and a mixed mode of the TE and TM modes can be used in the conventional wave guide, herein the TEM mode can not exist in a spherical or cylindrical wave guide but exist in a coaxial line or a twin-lead type feeder, etc.
However, in the conventional electrodeless discharge lamp using microwave energy, in order to transmit microwave energy outputted from a magnetron to a load side, a wave guide placed between a magnetron and a mesh screen and having a certain size in consideration of a standard of a transmission frequency, a TE mode or a TM mode is used or a cylindrical wave guide having a certain diameter is used.
Accordingly, in the conventional electrodeless discharge lamp using microwave energy, because it is impossible to reduce a size of a wave guide, it can not be used as a light source for a low-output system such as a LCD projector and a projection television, etc.